Use correct snapshot for the tab transition animation on iPad

ios/chrome/browser/ui/tab_switcher/tab_switcher_transition_context.mm

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ios/chrome/browser/ui/tab_switcher/tab_switcher_transition_context.h"
 
 #include "base/mac/objc_property_releaser.h"
 #import "ios/chrome/browser/tabs/tab.h"
 #import "ios/chrome/browser/ui/browser_view_controller.h"
 #include "ios/chrome/browser/ui/tab_switcher/tab_switcher_transition_context.h"
@@ skipping 14 matching lines @@
 @implementation TabSwitcherTransitionContextContent {
   base::mac::ObjCPropertyReleaser
       _propertyReleaser_tabSwitcherTransitionContextContent;
 }
 
 + (instancetype)tabSwitcherTransitionContextContentFromBVC:
     (BrowserViewController*)bvc {
   TabSwitcherTransitionContextContent* transitionContextContent =
       [[[TabSwitcherTransitionContextContent alloc] init] autorelease];
 
-  Tab* currentTab = [[bvc tabModel] currentTab];
-  transitionContextContent.initialSelectedTabIndex =
-      [[bvc tabModel] indexOfTab:currentTab];
+  transitionContextContent.initialTabID = bvc.tabModel.currentTab.tabId;
 
   if (![bvc isViewLoaded]) {
     [bvc ensureViewCreated];
     [bvc.view setFrame:[[UIScreen mainScreen] bounds]];
   }
 
   UIView* toolbarView = [[bvc toolbarController] view];
   base::scoped_nsobject<UIView> toolbarSnapshotView;
   if ([toolbarView window]) {
     toolbarSnapshotView.reset(
         [[toolbarView snapshotViewAfterScreenUpdates:NO] retain]);
   } else {
     toolbarSnapshotView.reset([[UIView alloc] initWithFrame:toolbarView.frame]);
     [toolbarSnapshotView layer].contents = static_cast<id>(
         CaptureViewWithOption(toolbarView, 1, kClientSideRendering).CGImage);
   }
   transitionContextContent.toolbarSnapshotView = toolbarSnapshotView;
   transitionContextContent->_bvc.reset(bvc);
   return transitionContextContent;
 }
 
 - (TabSwitcherTabStripPlaceholderView*)generateTabStripPlaceholderView {
   TabStripController* tsc = [_bvc tabStripController];
   return [tsc placeholderView];
 }
 
 @synthesize toolbarSnapshotView = _toolbarSnapshotView;
-@synthesize initialSelectedTabIndex = _initialSelectedTabIndex;
+@synthesize initialTabID = _initialTabID;
 
 - (instancetype)init {
   self = [super init];
   if (self) {
     _propertyReleaser_tabSwitcherTransitionContextContent.Init(
         self, [TabSwitcherTransitionContextContent class]);
   }
   return self;
 }
 
@@ skipping 34 matching lines @@
 - (instancetype)init {
   self = [super init];
   if (self) {
     _propertyReleaser_tabSwitcherTransitionContext.Init(
         self, [TabSwitcherTransitionContext class]);
   }
   return self;
 }
 
 @end